Various possibilities are known in the prior art for the relative adjustment of the angular position between the crankshaft and the camshaft of an internal combustion engine. Basically, electric and hydraulic adjusting systems are known. In the electrically driven camshaft adjustment systems, the relatively low torque of the electrical adjustment unit, for example a drive motor or a braking device, which is available in the case of a high rotational speed, is converted into a rotational movement with high torque; such a high torque is necessary for adjusting the camshaft. For this purpose, it is known to use summing gears as adjusting gears. Such a gear has a driving wheel fixed with respect to the crankshaft. Power take-off takes place via a gear output fixed with respect to the camshaft. The differential power of the gear which has to be fed in for adjustment in one direction of rotation or the other is introduced via a third shaft, the adjusting shaft, of the gear.
An electrical camshaft adjustor of this type is known from DE 102 48 355 A1. An adjusting device for the electrical adjustment of the relative rotary-angle position between the camshaft and the crankshaft is disclosed, a triple-shaft gear being used as the adjusting gear, which has a driving part fixed with respect to the crankshaft, a driven part fixed with respect to the camshaft and an adjusting shaft connected fixedly in terms of rotation to an adjusting-motor shaft for an electrical adjusting motor. The adjusting motor is designed, here, as a brushless direct-current motor with a stator fixed with respect to the housing and with a permanent-magnet motor. The adjusting gear used is a double eccentric gear or a double epicyclic gear, a reduction of up to 1:250 being provided here.
The relative adjustment of the camshaft with respect to the crankshaft is also described in other publications, use likewise being made of adjusting gears which can be actuated by an electric motor. EP 1 039 101 A2 uses a harmonic-drive gear as the adjusting gear. This gear operates with a thin elastically deformable toothed sleeve, the toothing of the sleeve meshing with a ring wheel. A compact type of construction of the adjusting gear, along with a high reduction ratio, is consequently possible.
Such a solution is also known from DE 40 22 735 A1, in which such a cycloidal reduction gear is used. A similar type of construction is shown in WO 95/00748.
U.S. Pat. No. 5,680,836 and DE 102 03 621 A1 use an epicyclic gear as the adjusting gear, in order to generate the relative rotation between the crankshaft and camshaft. Such a solution is also known from DE 25 25 746 A1.
The power flux is in this case to be capable of taking place with high efficiency during adjustment, so that the driving electric motor of the braking device can have as small a build as possible. As low a heat loss as possible is in this case to occur. Furthermore, the toothings of the adjusting gear are as far as possible to run, free of play, with respect to one another. If this is not so, during operation, undesirably high-pitched noises arise, the cause of which is primarily the highly variable alternating torque of the camshaft. Plays possibly occurring in the adjusting gear are converted according to the transmission ratio of the gear. It is additionally necessary for the construction space for the torque converter to have as small a configuration as possible, since there is a trend towards an ever more compact type of construction of the internal combustion engine. Furthermore, for safety reasons, certain distances between the body and the internal combustion engine must be adhered to, which likewise requires a compact type of engine construction. Moreover, the adjusting gear must be capable of being implemented as cost-effective as possible, so that the system costs for the electrical camshaft adjuster, consisting of adjusting gear, electric motor/brake and control electronics, can be kept low.
In the previously known solutions, there are, in this respect, restrictions, particularly with regard to quiet running. True-running errors of the toothings used can be kept low only at a high outlay, so that, during the engagement of gearwheels and during their rotation, some generation of noise is unavoidable. The lower the outlay in terms of manufacturing cost in the production of the gearwheels used is, the greater the problem of noise generation becomes.